Altadena, CA · West San Gabriel Valley
ADU construction prices in Altadena, CA: 2026 ranges
An ADU construction in Altadena costs $325–$540 per sq ft, with a typical mid-size ADU running $97k–$195k. Small projects start around $65k; large or high-end work can reach $486k or more.
As of 2026, costs in Altadena run about 8% above the LA County baseline due to Eaton Fire rebuilds and LA County rebuild permitting.
Updated
ADU Construction Cost by Size in Altadena
Totals adjusted for the Altadena market (1.08× LA County baseline). Ranges include labor, materials, permits, and contractor overhead.
| Size | Type | Range | Low | High |
|---|---|---|---|---|
| Small | JADU / studio | 150–400 sq ft | $65k | $141k |
| Medium | 1-bed garage conversion | 400–600 sq ft | $97k | $195k |
| Large | Detached 2-bed | 800–1,200 sq ft | $270k | $486k |
What Affects ADU Construction Cost in Altadena?
- ADU type (JADU vs attached vs detached).
- Site prep and grading.
- Utility connections.
- CA Title 24 energy compliance.
- City ADU permit timeline.
- Altadena market premium: local pricing reflects Eaton Fire rebuilds and LA County rebuild permitting, which shifts totals about 8% above the LA County baseline.
Get exact ADU construction bids in Altadena
Two or three licensed builders who work in Altadena, pricing the same scope.
ADU Construction Sub-Type Comparisons
Garage Conversion ADU vs Detached ADU
Garage conversions reuse the existing slab and shell at $90k–$180k; a detached new-build ADU runs $250k–$450k but unlocks larger floor plans and higher rent.
Junior ADU (JADU) vs Attached ADU
A JADU (≤500 sq ft, within the home) runs $60k–$130k and shares utilities; an attached ADU is a true second unit at $150k–$350k with its own entrance and meter.
How to Get the Best Price on a ADU Construction in Altadena
- Get line-itemized bids from two or three builders on the same scope; Altadena ADU construction pricing commonly varies 10–25% between contractors.
- Lock major materials and finishes before signing; mid-project change orders are the #1 cost driver on ADU construction jobs.
- Bid in shoulder seasons (Jan–Mar or Sep–Oct) when Altadena contractor schedules are open and rush premiums disappear.
- Verify CSLB license, insurance, and bond before paying any deposit. California caps deposits at $1,000 or 10% of contract, whichever is less.
What is an ADU construction?
An accessory dwelling unit (ADU) is a second, self-contained home on a single-family lot, with its own kitchen, bathroom and entrance. It can be detached, attached to the main house, a converted garage, or a junior ADU of up to 500 sq ft inside the existing home.
How to get an accurate price
- 1.Write down the scope: size, any layout changes, the finish level, and who supplies fixtures and materials.
- 2.Get bids from two or three licensed builders who work in Altadena, all pricing that same ADU construction scope.
- 3.Line the bids up item by item. Check allowances, permits, exclusions, and whether overhead and profit are shown.
- 4.Before any deposit, check each builder's CSLB license and insurance. As of 2026, California caps a home improvement down payment at $1,000 or 10% of the contract, whichever is less, according to the Contractors State License Board.
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Questions about ADU Construction in Altadena
How much does an ADU construction cost in Altadena, CA?
An ADU construction in Altadena costs $65k–$486k, with a typical mid-size ADU running $97k–$195k. Per-unit pricing falls in the $325–$540 per sq ft range.
Do I need a permit for an ADU construction in Altadena?
Yes for most scopes — LADBS or the local city building department requires permits any time you move plumbing, gas, electrical, or alter structure. Like-for-like cosmetic refreshes generally don't.
How long does an ADU construction take in Altadena?
Plan for 4–14 weeks of construction in Altadena depending on size and complexity, plus 2–8 weeks for design, permits, and material lead times.
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